In the process of hub's work, we know that there is only one physical signal transmission channel in the ring network, all of which are transmitted through a transmission medium, so there is a contradiction that all nodes compete for the channel and the transmission efficiency is low. After the introduction of hub, each site is connected to the hub through its own dedicated transmission medium, and there is no longer only one transmission channel between nodes. The signals sent back by each node are concentrated through the hub, which shapes and amplifies the signals and sends them to all nodes, so that at least there will be no collision on the uplink channel. However, the network based on hub is still a LAN with * * * media sharing, in which * * * sharing is actually the internal bus of hub, so there will still be signal conflicts when the uplink channel and the downlink channel send data at the same time. When the hub detects a collision from its internal port, it will generate a collision enhancement signal (Jam) and send it to the destination port to which the hub is connected. At this time, all data will not be sent successfully, forming a "big traffic jam" in the network. This network phenomenon can be illustrated by an image reality, that is, there are cars coming from two directions in a single lane at the same time, as shown in figure 1. We know that cars in one direction are usually allowed to pass in one lane, but in small towns, conditions are limited and there is usually no such regulation. It is also possible for cars in two directions to pass in one lane, but they must pass at different times. The same is true in the hub. Although each node has its own independent channel to connect with the hub, there is only one * * * channel inside the hub, and both uplink and downlink data must send and receive data through this * * * channel, which may be like a single lane. When uplink and downlink channels transmit data at the same time, traffic jams may occur. Easy to understand, right? Because of this shortcoming, the hub can't be used alone in a larger network (usually sharing a small part of the network communication load with switches and other devices), just like there can't be a one-way street in the center of a big city, because the more networks come, the greater the probability of network collision. For this reason, the data transmission efficiency of the hub is relatively low, because it can only transmit data in one direction at the same time, which is the so-called simplex mode. If the hub is used as a single hub device in the network, the network scale should be within 10, and the bandwidth of the hub should be above10100 Mbps. In addition to the lack of bandwidth, there is another aspect that must be considered when choosing a hub, that is, its broadcasting mode. Because the hub belongs to the bottom equipment of pure hardware network, it basically has no "intelligent memory" ability, let alone "learning" ability. It also has no MAC address table owned by the switch, so it sends data by broadcast, not as a target. That is, when it wants to send data to a node, it does not send data directly to the destination node, but sends data packets to all nodes connected to the hub, as shown in Figure 2. This way of sending data by broadcasting has two shortcomings: (1) User data packets are sent to all nodes, which easily brings about unsafe factors in data communication, and some people with ulterior motives can easily intercept other people's data packets illegally; (2) Because all data packets are sent to all nodes at the same time, plus the * * * bandwidth sharing mode described above, it is easier to cause network congestion and further reduce network execution efficiency.